You can't avoid what will happen, but you can have a say in how it happens.
Learning about your loved one's condition is one way to do something, to have a sense of taking action that puts you in the game rather than merely watching from the sidelines. Get a better idea of the symptoms, treatment options, and possible side effects so you can prepare for and even get ahead of what may be coming.
You could even help your loved one put their affairs in order or plan their funeral service.